Benzothiazyl sulfenamides in lubricants



Patented Feb. 16, 1954 BENZOTHIAZYL SULFENAMIDES IN LUBRICANTS Warren Lowe, Berkeley, Calif., :assignor to Cali- .fornia Research Corp Calif., .a corporation oration, San Francisco,

of Delaware 'No'Drawing. Application November 17, 1951, Serial No. 256,948

1-0 Claims.

The present invention relates to lubricating oil compositions containing sulfur which is corrosive to silver and like metals, which corrosion is inhibited by the presence oi benzothiazyl-sulfenamides, e. g. N-cyclohexyl-2 benzothiazyl .sulfenamide.

For the most part, internal combustion engines are operated at high speeds and at elevated temperatures, conditions which result in the formation of acidic products from the oxidation of lubricating oil. In addition to the acidic products resulting from the lubricating oil itself, oxidation of the engine fuel results in the formation of acidic bodies which find their way down into the lubricating oil chamber. Acidic products rapidly deteriorate the lubricating value of the oil and are severely corrosive to hard metal alloys such as cadmium-silver, copper-lead, etc. This corrosion resulting from acidic products, which corrosion may be called either acid corrosion or oxidation corrosion, is normally inhibited by the presence of oxidation inhibitors incorporated in the lubricating oil compositions.

A number of agents which are added to lubricating oils for the purposes of-improving various properties thereof contain sulfur. For example, aliphatic polysulfides, metal salts of organo thicphosphates, etc. are highly effective oxidation inhibitors, Other sulfur-containing agents such as sulfurized olefins, xanthatc esters and the like are excellent extreme pressure agents. The sulfur contained in these agents is severely corrosive to silver and like metals; however, this sulfur is not corrosive to such hard-metal alloys as cadmiumsilver alloy, which cadmium alloy normally contains less than 1% of silver. Where pure silver wearing surfaces are involved, the sulfur readily attacks the silver, resulting in a rapid darkening of the metal surfaces and the formation of sulfides. This results in a considerable pitting and loss of metal wearing surfaces.

As opposed to the corrosion and attack on metals by acidic bodies which is termed acid corrosion or oxidation corrosion, the corrosion caused by sulfur is designated herein as sulfur corrosion.

I In spite of the long desire to lubricate silver bearings with lubricants compounded with active sulfur compounds, it has been impractical to do so in view of the aforementioned severe corrosivity to silver.

Heretofore, in the lubrication of engines having silver metal-wearing surfaces, for example, in certain railroad diesel engines which use silver wrist pin bushings, it has been difilcult to prevent sulfur attack of the silver surfaces. Because the silver surfaces (e. g., the silver wrist pin bushings) are susceptible to attack by the sulfur of the sulfurcontaining lubricating oil additives, there has been a tendency to eliminate highly effective sulfur-containing additives from the diesel lubricating oils, thereby losing the remarkable benefits of these additives. As noted hereinabove, certain highly effective lubricating oil sulfur-containing anti-oxidants have not been used in diesel errgines containing silver wrist pin bushings without sulfur attack on the silver. Alternative pram tices have been to eliminate the sulfur-containing additives from the oil, allowing the oil to deteriorate more rapidly by oxidation; or the sulfurcontaining additives have been included in the oil formulations, with the resulting sulfur corrosion of the silver wrist pin bushings. Silver is also used for bearing surfaces in aircraft engines. but because of the presence of the silver, the highly effective sulfur-contaming aviation oil additives are not used. Now, however, by using the compounds of this invention, lubricating oil compounded with sulfur-containing additives can be used in diesel oils, aviation oils, and any other oils where sulfur corrosion of metals is a prob- 'lem.

Numerous agents have been proposed for inhibiting the sulfur attack on silver. It is, therefore, an object of this invention to set forth a new agent whichwill inhibit corrosion to silver by sulfur compounds.

According to the present invention, benzothiazyl sulfenamides inhibit sulfur attack on silver in lubricating oil compositions containing sulfur. The lubricants of this invention comprise a major portion of oils of lubricating viscosity, and minor amounts of benzothiazyl sulfenamides.

suitable base oils include a wide variety of lubricating oils such as naphthenic base, paraflin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oils derived from coal products, and synthetic oils, e. g. polysiloxane oils, alkylene polymers (such as polymers of propylene, butylene, etc. and mixtures thereof) alkylene oxide type polymers, dicarboxylic acid esters, liquid esters of acids of phosphorus, alkyl benzene polymers, etc. Synthetic oils of the alkylene oxide type polymers which may be used include those exemplified by the alkylene oxide polymers (e. g., propylene oxide polymers), and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxide, e. g., propylene oxide, in the presence of water or alcohols, c. g., ethyl alcohol; esters of alkylene oxide type polymers, e. g., acetylated propylene oxide polymers prepared by acetylating propylene oxide polymers containing hydroxyl groups; polyethers prepared from the alkylene glycols (e. g., ethylene glycol) etc. The polymeric products prepared from the various alkylene oxides and alkylene glycols may be polyoxyalkylene diols or polyalkylene glycol derivatives; that is, the terminal hydroxyl groups can remain as such, or one or both of the terminal hydroxyl groups can be removed during the polymerization reaction by etherification or esterification.

Synthetic oils of the dicarboxylic acid ester type include those which are prepared by esterifying such dicarboxylic acids as adipic acid, azealic acid, suberic acid, sebacic acid, alkenyl succinic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, Z-ethyl-hexyl alcohol, dodecyl alcohol, etc. Examples of the dicarboxylic acid ester synthetic oils include dibutyl adipate, dihexyl adipate, di-Z-ethyl-hexyl sebacate, di-N-hexyl furnaric polymer, etc.

Synthetic oils of the alkyl benzene type include those which are prepared by alkylating benzene (e. g., dodecyl benzene, tetradecyl benzene, etc.).

Synthetic oils of the type of liquid esters of acids of phosphorus include the esters of phosphoric acid, e. g., tricresyl phosphate; the esters of phosphonic acid, e. g., diethyl esters of decane phosphonic acid, or other such esters as obtained by reacting alkyl phosphonyl chlorides with hydroxyl-containing compounds such as phenyls and aliphatic alcohols, and with olefin oxides such as propylene oxide.

Polysiloxane oils (e. g., polymethyl siloxane, polymethyl phenyl siloxane, etc.) are particularly beneficial base oils where low temperatures and high temperatures are encountered in the lubricating oil compositions.

The improved lubricant of the present invention is used wherever elemental sulfur or sulfur compounds containing active sulfur attack metal and are severely corrosive to metals which are being lubricated. Lubricants which normally are severely corrosive to metal parts due to attack by sulfur or active sulfur compounds may now be used without fear of corrosion by incorporating therein 2-benzothiazylsulfenamides.

The agents of this invention useful for inhibiting corrosion of silver include the benzothiazyl sulfenamides of the formula:

sulfenamide, N-methylcyclohexyl-Z-benzothiazyl sulfenamide, N-ethyl 2 benzothiazyl sulfenamide, N-propyl-Z-benzothiazyl sulfenamide, N- butyl-Z-benzothiazyl sulfenamide, N-pentyl-2- benzothiazyl sulfenamide, N-2,3-dimethylhexyl- .Z-benzothiazyl sulfenamide, N-hexyl-2-benzothiazyl sulfenamide, N-heptyl-Z-benzothiazyl sulfenamide, N-octyl 2 benzothiazyl sulienamide, etc..

I. It'. is preferred to use N-cyclohexy1-2-benzo thiaz'yl sulfenamide.

For inhibiting corrosion to silver caused by Sulfur, the benzothiazyl sulfenamides of this invention are effective when used in amounts as low as 0.01% and as great as about 10% by weight of the total composition. However, it is preferred that the compounds of this invention be used in amounts suflicient substantially to reduce the corrosion to silver. For example, it is preferred to use the benzothiazyl sulfenamides in amounts of from about 0.05% to about 0.50%. The major proportion of the lubricating oil composition of this invention is the base oil.

In order to evaluate the agents of this invention for inhibiting corrosion due to active sulfur, silver strip corrosion tests were made. These silver strip corrosion tests were performed as follows:

A silver metal strip having the dimensions of 2%.; inches by A. with a wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly-polished silver strip was then placed in a 600 ml. beaker in such a man ner that the strip was completely immersed when 300 grams of the oil being tested was poured into the beaker. perature of 300 F. for 20 hours, at which time the silver strip was removed and cleaned, first with chloroform, then with petroleum ether. The appearance of the strip was noted. Those strips which had been severely attacked were quite black. The tested silver strips were washed in 15% aqueous solution of potassium cyanide for about 5 minutes to remove the sulfide film adhering to the strip. After the strip had been washed with potassium cyanide and dried, it was Weighed. The difference in weight of the original strip and the strip after the potassium cyanide wash was noted and recorded as the weight loss due to corrosion by the sulfur compound.

The data below show the remarkable effect of benzothiazyl sulfenamides in reducing the attack on silver.

The data of Table I were obtained in the silver strip test, using a California solvent-refined SAE 30 paraffinic base oil containing N-cyclohexyl- 2-benzothiazyl sulfenamide, 0.9 millimole percent of a zinc alkylphenyl dithiophosphate, 0.7 millimole percent of a calcium alkylbenzene sulfonate, and 1.6 millimole percent of a sulfurized calcium alkylphenate. The alky radical in these additives was derived from a mixture of propene and butene polymers, and contained an average of 14 carbon atoms.

Table I Amount of N-cyclohexyl Silver Strip Y 2-Benzothiazyl- Test (Weight rest Sulfenamide Loss in Milli- (Percent by grams) weight) The following Table II shows the effectiveness of N-cyclohexyl-2-benzothiazyl-sulfenamide in reducing the silver corrosivity of an oil composi-- tion containing 0.5% by weight of a sulfurized olefin, 0.9 millimole percent of a calcium alkylbenzene sulfonate, and 0.9 millimole percent of amine alkylbenzenedithiophosphate in a base oil consisting of' 4.5% byweight of a polypropylene; glycol octylether acetate and 54.5%by weight of a California solvent refined paraffim'c inch by 2 inch was first cleaned The oil was stirred at a tembase lubricating oil. The alkyl radical is the same as that defined above.

The following Table III illustrates still further the effectiveness of benzothiazyl-sulfenamides in reducing the silver corrosivity of lubricating oil compositions. The alkyl radicals of the additives in the oil are the same as those defined hereinabove in Table I.

Table III Amount of N-cyclohexyl- Silver Strip Test N0 Reference Benzothiazyl- Test (Weight Oil Sulfenamide Loss in Milli- (Percent by grams) Weight) 1 California solvent-refined SAE paraliinic base lubricating oil containing 0.7 millimole percent of a calcium alkylbenzene sulfonate 1.6 millimole percent of a sulfurizcd calcium alkylphenate and 0.016% by weight of sulfur.

California solvent-refined SAE 30 base oil containing 0.7 millimcle percent of a calcium alkylbenzenc sulfonate, 1.6 millirnole pleigent of a sulfurized calcium alkylphenate plus 0.5% of a sulfurizcd o c n a California solvent-refined SAE 30 paraffiuic base lubricating oil containing 0.7 millimole percent of a calcium alkyl-benzene sulfouate, 1.6 millimole percent of a sulfurized calcium alkylphcnate and 0.1% by weight of sulfur.

4 California solvent-refined base SAE 30 paraflinic base lubricating oil containing 0.7 millimole percent of a calcium alkylbenzene sulfonate, 1.6 millimole percent of a sulfurlzed calcium alkylphenate plus 1% by weight of a sulfurized olefin.

wherein R is a radical selected from the group consisting of alicyclic and aliphatic radicals.

2. A lubricant consisting essentially of a major proportion of an oil of lubricating viscosity having incorporated therein sulfur-containing additives which are corrosive to silver, which additives inhibit corrosion caused by oxidation, and from 0.01% to of a benzothiazyl sulfenamide of the formula wherein R is a radical selected from the group consisting of alicyclic and aliphatic radicals.

3. A lubricant consisting essentially of a major proportion of an oil of lubricating viscosity having incorporated therein sulfur-containing C0111- pounds having sulfur corrosive to pure silver wearing surfaces, and from about 0.01% to 10% of a benzothiazyl sulfenamide of the formula wherein R is a radical selected from the group consisting of alicyclic and aliphatic radicals.

4. The lubricant of claim 3, wherein the benzothiazyl sulfenamide is an N-alicyclic-z-benzothiazyl sulfenamide.

5. The lubricant of claim 3, wherein the benzothiazyl sulfenamide is an N-aliphatic-2-benzothiazyl sulfenamide.

6. The lubricating oil composition of claim 3. wherein the benzothiazyl sulfenamide is N-cyclohexyl-2-benzothiazyl sulfenamide.

7. A lubricating oil composition at least of which is composed of an admixture of an oil of lubricating viscosity and lubricating oil additives having present sulfur corrosive to pure silver, said additives inhibiting corrosion due to oxidation, and compounded with this mixture from about 0.01% to about 10% of a benzothiazyl sulfenamide of the formula wherein R is a radical selected from the group consisting of alicyclic and aliphatic radicals.

8. A lubricating oil composition at least 95% of which is composed of an admixture of an oil lubricating viscosity and lubricating oil additives having present sulfur corrosive to pure silver, said additives inhibiting corrosion due to oxidation, and compounded with this mixture an N-cyclohexyl-2-benzothiazyl sulfenamide in an amount sufiicient to inhibit corrosion to silver by the sulfur.

9. A lubricating oil composition at least 95% of which is composed of an oil of lubricating viscosity and lubricating oil additives having present sulfur which is corrosive to pure silver, and from 0.05% to 0.50% by weight of a benzothiazyl sulfenamide of the formula wherein R is a radical selected from the group consisting of alicyclic and aliphatic radicals.

10. A lubricating oil composition at least 95% of which is composed of an oil of lubricating viscosity and lubricating oil additives having present sulfur which is corrosive to pure silver, and from 0.05% to 0.50% by weight of N-cyclohexyl-2-benzothiazyl sulfenamide.

WARREN LOWE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,154,097 Laone Apr. 11, 1939 2,218,283 Fuller Oct. 15, 1940 2,271,834 Carr Feb. 3, 1942 

1. A LUBRICANT CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A SILVER CORROSIVE SULFUR-CONTAINING LUBRICATING OIL COMPOSITION, AND FROM ABOUT 0.01% TO ABOUT 10%, BY WEIGHT, OF A BENZOTHIAZYL SULFENAMIDE OF THE FORMULA 